Overload device for lift truck

ABSTRACT

A tilt ram connecting pin is elongated in one axial direction so that a small deflection of the pin at its connection with the tilt ram will produce a much larger deflection of the pin at a point on the elongated part remote from such connection. A motion multiplying lever contacts the pin at such point and operates a switch which operates a warning signal device such as a warning light and/or prevents operation of the lift truck while unsafe or prevents movement of the load or mast in a manner that would make operation of the truck less safe.

United States Patent 10 Claims, 3 Drawing Figs.

U.S. Cl 214/673 B66f 9/20 Field of Search 214/670- References Cited UNITED STATES PATENTS 3,031,094 4/1962 Arnot 214/674 Samuel T. Comfort l-lomewood;

Thomas J. Finlayson, Forest Park, Ill. 848,825

Aug. 1 l, 1969 Mar. 16, 1971 Allis-Chalmers Manufacturing Company Milwaukee, Wis.

Inventors Appl. No. Filed Patented Assignee OVERLOAD DEVICE FOR LIFT TRUCK 3,032,221 5/1962 Carlissetal. 3,203,672 8/1965 Santos Primary Examiner-Gerald M. Forlenza Assistant Examiner-Raymond B. Johnson Attorneys-Charles L. Schwab, Robert B. Benson and Kenneth C. Mc Kivett ABSTRACT: A tilt ram connecting pin is elongated in one axial direction so that a small deflection of the pin at its connection with the tilt ram will produce a much larger deflection of the pin at a point on the elongated part remote from such connection. A motion multiplying lever contacts the pin at such point and operates a switch which operates a warning signal device such as a warning light and/or prevents operation of the lift truck while unsafe or prevents movement of the load or mast in a manner that would make operation of the truck less safe.

OVEQAD DEVICE FQR LIFT TRUCK This invention relates to means to assist the lift truck operator in following safe lift truck operating practices. More specifically, the invention relates to an overload device which senses forward overturning moment and upon the moment approaching an unsafe overturning condition operates a signal or control to incapacitate the truck or operating controls thereof.

Overload detecting systems have heretofore been suggested for lift trucks which employ means associated with a tilt ram to sense the tilting moment to which a counterbalanced lift truck is subjected. Devices heretofore proposed have lacked the sensitivity desired which requires such devices to be set at mo ment much lower than the actual safe limit for the truck with the result that the truck cannot be used to its actual safe load capacity. Also, some prior art moment sensing devices have required excessive space for installation, require frequent readjustment and/or are excessively accessible to the truck operator or others permitting misadjustment or disabling of the device contrary to the desire of the owner.

The purpose of this invention is to provide an overload signal device which requires a small amount of space, is rugged, reliable, relatively inexpensive and is sensitive to a small movement so as to allow the safety device with which associated to be set at a higher safe limit than heretofore feasible.

More specifically it is an object of this invention to provide a deflecting connecting pin. for a lift truck tilt ram with an elongation at one end whereby a small deflection at the point of connection with the tilt ram results in a multiplied deflection of the elongated portion.

in applying the present invention to a lift truck, the connecting pin for the tilt ram is rigidly secured to the truck at its opposite ends with the tilt ram pivotally connected adjacent the laterally outer end. The pin is tapered from the ram connection to the laterally inner end so as to provide a uniform stress loading over the tapered portion of the pin. This provides for maximum pin deflection for operating the control device yet sufficient strength for the ram connecting mission of the pin. In order to provide a second multiplication of movement, a lever is provided at right angles to the part of the tapered pin which has maximum deflection. The lever is secured at one end to the truck chassis and contacts the pin at about its midpoint. The free end of the lever operates a microswitch in a signal or control circuit.

The invention and its objects having been broadly described, a more detailed description follows in which reference is made to the drawings in which:

FIG. 1 is a side view of a lift truck in which the present invention is incorporated;

FIG. 2 is a section view of the overload device of this invention taken along the line 11-11 in FIG. 1; and

FIG. 3 is a section view taken along the line ill-Ill in FIG. 2.

The overload sensing device of this invention is of particular utility'in a counterbalanced lift truck of the type illustrated in F 1G. 1 wherein a mast 11 is pivotally connected to the chassis 12 of the lift truck 13 by suitable pins for tilting movement about transverse axis 16. The mast i1 is provided with a suitable lift ram i7, the cylinder of which rests on a transverse bottom plate 18 of the outer, nonextensible mast section 19 and the rod end of the lift ram 17 is connected to the inner mast section 21 and supports the lift carriage 22 through a conventional pulley and lift chain arrangement. The channel members 24, 26 of the outer mast section are also rigidly interconnected in a conventional manner by cross braces 27, 28. As shown in FIGS. 1 and 2, fore and aft tilting movement of the mast about transverse axis 16 is controlled by a pair of tilt rams 31, 32 having their rods 33, 34 pivotally connected to the outer section T9 of the mast by pins 36, 37. The cylinders 38, 3? of the tilt rams 31, 32 have their rearwardly extending flanges 48, 561? pivotally connected to the chassis 12 by anchor pins ll, 45.

As shown in the drawings, pin 41 is of unique design to perform a sensitive overload control function. Adjacent enlarged portions 42, 43 of pin 41 fit snugly in bores 44, 46 of bracket 47 and flange The pin 41 is uniformly tapered from portion as to its small diameter portion 49 which is rigidly secured to chassis 112 by a split bearing having a cap 51 secured to its base part 52 by a pair of capscrews 53, only one of which is shown.

Referring also to FIG. 3, when the forward tilting moment of the mast and its load reaches a FIG. at which it is desired to signal the operator, disable a control function or otherwise affect operation of the truck, the pin 41 will have deflected in a forward arc sufiiciently to permit the sprung lever 56 to actuate the switch 57 through movement of switch button 58. The switch 57 and lever 56 are both rigidly secured to a bracket 59 which in turn is rigidly secured to the chassis 12 as by cap screws 61. The lever 56 is designed to resiliently bend at a reduced cross section portion 62 which acts as a metal hinge. in the condition illustrated in FIG. 3, the truck is lightly loaded and the pin is only slightly deflected. The pin 41 is formed with a uniformly tapered portion 66 to provide a fairly uniform stressing thereof which results in a relatively uniform deflection curvature. The midpoint of biased lever 56 contacts the midpoint of the tapered portion 66 which is the pin's approximate maximum deflection point. Thus, a minor deflection of the pin at the portion 43 contacting the cylinder flange 48 will produce a much greater deflection at the point of contact with the lever 56. This magnified deflection is further multiplied by the lever 56 so as to provide sufficient motion at the free end 67 of the lever to achieve a proper sensitivity in operation of commercially available microswitch 57. The switch 57 will operate upon two-thousandths of an inch deflection. The switch is initially positioned on bracket 59 so as to be actuated upon a predetermined deflection of the pin 41 which occurs upon a predetermined forward tilting moment about axis 16. The slotted opening 68 for bolt 69 allows the switch 57 to be adjusted on the bracket 59 for initial or subsequent adjustment as to the safe load limit.

From the foregoing description it is seen that a novel load indicating device has been provided in one of the pivotal connecting means for a tilt ram. By using an elongated transverse connecting pin between the cylinder end of the tilt ram and the chassis, themechanism is disposed beneath the floorboard 91 of the truck at a remote inner part of the lift truck chassis which is relatively inaccessible to the operator orothers. Also, the wiring associated with the switch 57 is located on a stationary part of the chassis. The illustrated embodiment of the invention does not necessitate major modification of the truck, is compact, relatively simple in construction and inexpensive to provide either as standard or optional equipment. The illustrated embodiment is rugged in design and sensitive in function, permitting operation in a plus or minus 5 percent range. in the mechanism itself, pivotal joint wear is avoided by using a metal hinge-type lever 56 which is prebent to resiliently contact the pin 41 over its deflection range. The design of the lever 56 is such that substantially all of the hinging action takes place in the reduced section portion 62. The bracket 92 is not required for operation of the mechanism but is standard equipment in case the mechanism of this invention removed and a standard connecting pin is used in place thereof.

We claim:

1. in a counterbalanced lift truck having a chassis, a mast pivotally mounted on said chassis for fore and aft tilting movement, a tilt ram for tilting said mast assembly, a first pivotal connecting means connecting one end of said ram to said mast, and a second pivotal connecting means connecting the other end of said ram to said chassis, a load indicating device comprising:

a transverse resilient pivot pin constituting a part of said second pivotal connecting means having;

relatively adjacent connecting portions in load transmitting engagement with said chassis and ram, respectively;

an elongated portion extending axially in one direction from said portions;

means connecting the end of said elongated portion remote from said connecting portions to said chassis whereby the application of tilting moment to said mast results in deflection of said elongated portion of said pin; and

control means operatively associated with the elongated portion of said pin and actuated upon movement thereof to effect a signal and/or operate a lift truck control means.

2. The invention of claim 1 in which said elongated portion is tapered in said one direction to a reduced cross section.

3. The invention of claim 1 wherein said connecting portion of said pin in load transmitting engagement with said ram is between the other of said connecting portions and said elongated portion.

4. The invention of claim 3 in which said elongated portion is tapered in said one direction to a reduced cross section.

5. The invention of claim 1 in which said control means includes a lever having one end mounted on said chassis and having a portion intermediate its ends in contact with said elongated portion so as to move in response to deflection of said pin.

6. The invention of claim 5 wherein said lever is disposed in transverse relation to said pin.

7. The invention of claim 6 wherein said control means includes a switch actuated by. motion of said lever.

8. The invention of claim 7 wherein the other end of said lever actuates said switch whereby the motion of said other end of said lever is a multiplication of the deflection of said elongated portion of said pin.

9. The invention of claim 8 wherein said elongated portion is tapered in said one direction to a diminishing cross section.

10. The invention of claim 9 wherein said connecting portion of said pin in load transmitting engagement with said ram is between the other of said connecting portions and said elongated portion. 

1. In a counterbalanced lift truck having a chassis, a mast pivotally mounted on said chassis for fore and aft tilting movement, a tilt ram for tilting said mast assembly, a first pivotal connecting means connecting one end of said ram to said mast, and a second pivotal connecting means connecting the other end of said ram to said chassis, a load indicating device comprising: a transverse resilient pivot pin constituting a part of said second pivotal connecting means having; relatively adjacent connecting portions in load transmitting engagement with said chassis and ram, respectively; an elongated portion extending axially in one direction from said portions; means connecting the end of said elongated portion remote from said connecting portions to said chassis whereby the application of tilting moment to said mast results in deflection of said elongated portion of said pin; and control means operatively associated with the elongated portion of said pin and actuated upon movement thereof to effect a signal and/or operate a lift truck control means.
 2. The invention of claim 1 in which said elongated portion is tapered in said one direction to a reduced cross section.
 3. The invention of claim 1 wherein said connecting portion of said pin in load transmitting engagement with said ram is between the other of said connecting portions and said elongated portion.
 4. The invention of claim 3 in which said elongated portion is tapered in said one direction to a reduced cross section.
 5. The invention of claim 1 in which said control means includes a lever having one end mounted on said chassis and having a portion intermediate its ends in contact with said elongated portion so as to move in response to deflection of said pin.
 6. The invention of claim 5 wherein said lever is disposed in transverse relation to said pin.
 7. The invention of claim 6 wherein said control means includes a switch actuated by motion of said lever.
 8. The invention of claim 7 wherein the other end of said lever actuates said switch whereby the motion of said other end of said lever is a multiplication of the deflection of said elongated portion of said pin.
 9. The invention of claim 8 wherein said elongated portion is tapered in said one direction to a diminishing cross section.
 10. The invention of claim 9 wherein said connecting portion of said pin in load transmitting engagement with said ram is between the other of said connecting portions and said elongated portion. 